I have a 2011 A6 Allroad Avant 3.0L diesel with 175000 miles on it. It's a good runner.

About 2 months ago I noticed a droning sound that starts at 40mph. It's very gradually getting noisier but only to me, my passengers don't make comment, they probably think it's just an 'old car'  noise, but I know my car can be quieter. The noise increases a little as my speed increases beyond 40mph a little but it's not deafening. As I slow down the noise winds down. It's more noticeable on left hand bends, and goes a little quieter on right hand bends. The F/N/S bearing was replaced in October 2023, 22K miles ago, with an SKF brand bearing. My mechanic is leaning towards the noise being created by the front discs, however the pads were replaced about 4 months ago, 2 months before the droning started, and the braking is good even from high speeds. My question to the forum is, how can we determine which wheel might need a new bearing? With it being a 4xwheel drive, there's no non driving wheels to rule them out. Is there any way of pinning down which bearing it might be? Thanks in anticipation. 👍

Does your mechanic not know how to test a wheel bearing?

In essence you jack the wheel up clear of the ground. Roll it while listening for a rumbling or grinding sound, then rock it side to side feeling and listening for movement.

Having changed the F/N/S bearing two years ago it's likely the other side needs to be changed.

54 minutes ago, Brian Howard said:

I have a 2011 A6 Allroad Avant 3.0L diesel with 175000 miles on it. It's a good runner.

About 2 months ago I noticed a droning sound that starts at 40mph. It's very gradually getting noisier but only to me, my passengers don't make comment, they probably think it's just an 'old car'  noise, but I know my car can be quieter. The noise increases a little as my speed increases beyond 40mph a little but it's not deafening. As I slow down the noise winds down. It's more noticeable on left hand bends, and goes a little quieter on right hand bends. The F/N/S bearing was replaced in October 2023, 22K miles ago, with an SKF brand bearing. My mechanic is leaning towards the noise being created by the front discs, however the pads were replaced about 4 months ago, 2 months before the droning started, and the braking is good even from high speeds. My question to the forum is, how can we determine which wheel might need a new bearing? With it being a 4xwheel drive, there's no non driving wheels to rule them out. Is there any way of pinning down which bearing it might be? Thanks in anticipation. 👍

Hi I would tend to agree with your mechanic as most people tend to forget the fact that when discs get older they tend to warp a fraction say a few thou and baring in mind the running tolerance free is only about 0.5 mm this would cause the symptoms you describe.

Steve. 

1 hour ago, cliffcoggin said:

Does your mechanic not know how to test a wheel bearing?

In essence you jack the wheel up clear of the ground. Roll it while listening for a rumbling or grinding sound, then rock it side to side feeling and listening for movement.

Having changed the F/N/S bearing two years ago it's likely the other side needs to be changed.

Hi Cliffcoggin. Thanks for responding. With it being a 4x wheel drive I would have thought that trying to rotate the wheel fast enough (Equivalent to 40mph) would have been impossible by hand. (I'm no expert on this, that's why I am here!). Even in neutral, rotating the wheel would still engage some parts of the gearbox, wouldn't they? I accept that there may be some play in the wheel if it's bad enough. 

Steve. Thanks for replying. If it is the discs, would this fault have just developed gradually over time, as it appears to have done?

You don't have to rotate the wheel quickly, not does it matter if the transmission is connected. It is the sound and feel of a worn bearing that you are trying to detect, not the resistance to motion.

If I can find a tyre fitters that has one of those little toboggans that they sit on and roll up to a jacked up wheel to rotate it for wheel balancing, would that do the automatic gearbox any harm? It's the only thing I can think of that would get the wheel rotating fast enough. 

32 minutes ago, cliffcoggin said:

You don't have to rotate the wheel quickly, not does it matter if the transmission is connected. It is the sound and feel of a worn bearing that you are trying to detect, not the resistance to motion.

Thanks Clifford. I will give it a try myself. I have a trolley jack. 

It's quite difficult to determine a wheel bearing on a quattro in my experience. I've rarely identified a wheel bearing based on holding the road wheel at 10 to 2 position or trying lateral movement. In addition I don't think it's the brakes. You can generally rule out the brakes and a sticky piston by driving for a few miles and coast to a stop. A sticky piston or contact on the pads and the disc and will heat up rapidly.

Normally I've had to strip down the brakes to get to the hub, then rotate. It's normally fairly obvious at that point. If you've already renewed the N/S/F, then chances are the O/S/F if it's original has gone. Pretty sure SFK and F.A.G. are the same plant. I tend to opt for F.A.G. given labour to replace.

Now the hard work - this can be done on a drive, but a word of warning - that bearing hub will be corroded to the strut housing with aluminium oxide. You'll need a air hammer or similar to shift it.  The front axle hub bolt will need be torqued up too, so make sure you have a 3/4" breaker bar. 1/2" will likely bend or break.

Dave Sterl does a cracking video to millustrate. 

 

Edited November 24, 2025Nov 24 by spartacus 68

11 hours ago, Brian Howard said:

Hi Cliffcoggin. Thanks for responding. With it being a 4x wheel drive I would have thought that trying to rotate the wheel fast enough (Equivalent to 40mph) would have been impossible by hand. (I'm no expert on this, that's why I am here!). Even in neutral, rotating the wheel would still engage some parts of the gearbox, wouldn't they? I accept that there may be some play in the wheel if it's bad enough. 

You'd definitely be involving the diffs and transfer boxes.  It's nigh on impossible to rotate a wheel by hand to any great effect.  Would it be possible to lift a complete axle off the ground and run the car in gear ,just on tick over ??  

Clifford/Richard/Billy. 

Thank you all for responding. 

Clifford, This morning I have jacked up the wheels in turn and I found I could not rotate the wheels fast enough to get any noise out of them. They just seem to be too heavy to get any meaningful rotation in them. As soon as I stop turning them, they only go about half a rotation then stop. I gripped and tried to rock them but could not detect any movement. 

Billy. If I were to lift the wheels of one axle up, the other two wheels would still want to drive off as it's a quattro. 

Richard. Thanks for the info and video. It is good, but way beyond my ability. Good to see it though. It's a lot more involved than I thought.

 

19 hours ago, Brian Howard said:

Steve. Thanks for replying. If it is the discs, would this fault have just developed gradually over time, as it appears to have done?

Hi yes the fault will develop gradually especially if the discs have not been replaced recently, I have owned cabs now for over twenty years and regardless of make/model the braking systems are virtually the same just different size components , I can tell you one thing when a bearing is on its way out even spinning the wheel slowly you can feel the drag of the dried ball races before you hear it, discs on the other hand have on occasions plagued me sometimes especially when you get a local garage to supply and fit because I was recovering from an operation these particular gems known as NAPA, the rears were ok but the pads wore in record time as did the fronts with the added bonus of the front discs warping after 20k just enough to make noises no judder, this also manifested itself on occasions with better quality discs/pads but the underlying factor was they had done 40k hard miles, regardless of milage age is also a factor.

Steve.

2 hours ago, Brian Howard said:

Clifford/Richard/Billy. 

Thank you all for responding. 

Clifford, This morning I have jacked up the wheels in turn and I found I could not rotate the wheels fast enough to get any noise out of them. They just seem to be too heavy to get any meaningful rotation in them. As soon as I stop turning them, they only go about half a rotation then stop. I gripped and tried to rock them but could not detect any movement. 

Billy. If I were to lift the wheels of one axle up, the other two wheels would still want to drive off as it's a quattro. 

Richard. Thanks for the info and video. It is good, but way beyond my ability. Good to see it though. It's a lot more involved than I thought.

 

 

Jack the wheels up diagonally then.  Then do the other 2 .  It shouldn't move.